This invention relates to a safety device for a hinge employed by a rotary member such as in an office machine (especially a duplication machine) wherein a moment varies corresponding to a rotation angle.
In a lid body, especially in a device employed for opening or closing the lid of a duplication machine having a weight of several pounds, a force is necessary to prevent an accident such as catching an operator's fingers or hitting of a foot due to the falling of the lid body. It has been a problem for a long period of time, to those skilled in the art, to solve this problem.
The following hinge device is provided in order to solve this problem.
The conventional hinge device, for instance, is shown in FIGS. 1(a), 1(b) and 1(c). In FIG. 1, the numeral 1 is a fixed member, and a core bar 2 is secured to erected plates 1a and 1b of said fixed member with bolts 6 restraining the rotation around an axial center. A lid body 3 or its attached member (hereafter called "lid body") is supported by said core bar 2 rotatively, and between the lid body 3 and the core bar 2, a spiral spring 4 is provided. Further, numeral 5 is a belleville spring and numeral 7 is an abutment plate which serves as a washer. This hinge device is designed so that the overall characteristics of a spring torque on the spiral spring 4 and a friction force of the belleville spring 5 may be approximately equivalent to a rotational moment of the lid body 3 when the lid body 3 opens from a closing status in FIG. 1(a) in the direction of a'.
FIG. 7 shows this relationship. In FIG. 7, S shows a characteristic of the spring torque of the spiral spring 4, L shows the moment of the rotation of the lid body 3 and F shows the friction force of the belleville spring 5. Although the spiral spring 4 is designed so that the spring torque characteristic S may correspond to the moment of the rotation of the lid body 3, it is impossible to make it correspond through the whole range of rotation of the lid body 3. Therefore, in this hinge device, the deviation between the spiral torque characteristic S and the moment of rotation is designed so that it may be smaller than the friction force F of the belleville spring 5, and said deviation amount is adapted to be absorbed with the friction force 4. Thus, the overall characteristic of the spring torque S of the spiral spring 4 and the friction force F of the belleville spring 5 can be approximated to the moment of the rotation L, of the lid body 3, over the whole range of the lid body 3.
In the invention of the present hinge device, together with being capable of an operation force necessary for rotation of the lid 3a, the lid body may be stopped at an arbitrary position within a range of operation.
In the prior art hinge device, however, when the spiral spring 4 is broken, the lid body 3 openings upwards, falls down rapidly, thereby causing an accident such as catching an operator's fingers or the like.